Best metalsmithing huddle on the Internet, is by far, Ganoskin. Ask about green metal in their forum area, and I would not doubt you would get your answer. I see people from the outside ask the pros there questions, all the time. The people there are jewelers and well-known metalsmiths -- not your average hobbyist who has taken a simple class or two. http://www.ganoksin.com/orchid/orchid.htm

Also, do a search in the forum archives. I could swear, I've seen them talk about colored metals (oranges, greens, blues, etc). . If not - I saw it in Lapidary Journal. I'm going to do a looksee through mine for you...